Gravity Probe B Confirms Two Einstein Theories

WASHINGTON -- NASA's Gravity Probe B (GP-B) mission has confirmed two
key predictions derived from Albert Einstein's general theory of
relativity, which the spacecraft was designed to test.

The experiment, launched in 2004, used four ultra-precise gyroscopes
to measure the hypothesized geodetic effect, the warping of space and
time around a gravitational body, and frame-dragging, the amount a
spinning object pulls space and time with it as it rotates.

GP-B determined both effects with unprecedented precision by pointing
at a single star, IM Pegasi, while in a polar orbit around Earth. If
gravity did not affect space and time, GP-B's gyroscopes would point
in the same direction forever while in orbit. But in confirmation of
Einstein's theories, the gyroscopes experienced measurable, minute
changes in the direction of their spin, while Earth's gravity pulled
at them.

The findings are online in the journal Physical Review Letters.

"Imagine the Earth as if it were immersed in honey. As the planet
rotates, the honey around it would swirl, and it's the same with
space and time," said Francis Everitt, GP-B principal investigator at
Stanford University. "GP-B confirmed two of the most profound
predictions of Einstein's universe, having far-reaching implications
across astrophysics research. Likewise, the decades of technological
innovation behind the mission will have a lasting legacy on Earth and
in space."

GP-B is one of the longest running projects in NASA history, with
agency involvement starting in the fall of 1963 with initial funding
to develop a relativity gyroscope experiment. Subsequent decades of
development led to groundbreaking technologies to control
environmental disturbances on spacecraft, such as aerodynamic drag,
magnetic fields and thermal variations. The mission's star tracker
and gyroscopes were the most precise ever designed and produced.

GP-B completed its data collection operations and was decommissioned
in December 2010.

"The mission results will have a long-term impact on the work of
theoretical physicists," said Bill Danchi, senior astrophysicist and
program scientist at NASA Headquarters in Washington. "Every future
challenge to Einstein's theories of general relativity will have to
seek more precise measurements than the remarkable work GP-B
accomplished."

Innovations enabled by GP-B have been used in GPS technologies that
allow airplanes to land unaided. Additional GP-B technologies were
applied to NASA's Cosmic Background Explorer mission, which
accurately determined the universe's background radiation. That
measurement is the underpinning of the big-bang theory, and led to
the Nobel Prize for NASA physicist John Mather.

The drag-free satellite concept pioneered by GP-B made a number of
Earth-observing satellites possible, including NASA's Gravity
Recovery and Climate Experiment and the European Space Agency's
Gravity field and steady-state Ocean Circulation Explorer. These
satellites provide the most precise measurements of the shape of the
Earth, critical for precise navigation on land and sea, and
understanding the relationship between ocean circulation and climate
patterns.

GP-B also advanced the frontiers of knowledge and provided a practical
training ground for 100 doctoral students and 15 master's degree
candidates at universities across the United States. More than 350
undergraduates and more than four dozen high school students also
worked on the project with leading scientists and aerospace engineers
from industry and government. One undergraduate student who worked on
GP-B became the first female astronaut in space, Sally Ride. Another
was Eric Cornell who won the Nobel Prize in Physics in 2001.

"GP-B adds to the knowledge base on relativity in important ways and
its positive impact will be felt in the careers of students whose
educations were enriched by the project," said Ed Weiler, associate
administrator for the Science Mission Directorate at NASA
Headquarters.

NASA's Marshall Space Flight Center in Huntsville, Ala., managed the
Gravity Probe-B program for the agency. Stanford University, NASA's
prime contractor for the mission, conceived the experiment and was
responsible for the design and integration of the science instrument,
mission operations and data analysis. Lockheed Martin Corp. of
Huntsville designed, integrated and tested the space vehicle and some
of its major payload components.